A locking system provides the following actions: locking a mobile telephone to the services of a particular operator; locking a mobile telephone to particular services of a given operator; and locking a mobile telephone to a given SIM card microchip to prevent the use of the mobile telephone with a microchip card other than that with which the telephone was sold.
The locking system generally allows an operator to ensure that a customer who has purchased a telephone in the context of a promotion, whereby the telephone is sold at a very much reduced price on condition that the customer uses a particular subscription for a relatively long period, will comply with the terms of his agreement. This also solves other problems, for example the use of a stolen telephone with another microchip card.
It is nevertheless necessary to provide means for canceling such                locking, for example at the end of an agreement.        
A specific piece of information referred to hereinafter as the locking key is introduced into the telephone by the manufacturer during its manufacture, and problems with unlocking relate essentially to relations between the user of the telephone and the telephone operator, the standard practice being for a manufacturer to communicate a list of keys to an operator. The latter then carries out the unlocking at the request of the user, after verifying the latter's rights.
Transferring unlocking keys necessitates secure communication between manufacturers and operators.
As there is generally no exclusive agreement between them, each manufacturer supplies all operators, and vice-versa. Communication is not secure.
Furthermore, the number of telephone designs increases daily. There are therefore serious communication problems that lead to serious malfunctions and a very large number of complaints from users.